Atoms with 1,2, or 3 electrons in their outer shell tend to be electron donors since their affinity for electrons is relatively low.  It takes too much energy to pull away 5, 6, or 7 electrons to obtain a filled outer shell.  On the other hand, atoms with 5, 6, or 7 electrons in their outer shell tend to be electron acceptors; they have a high affinity for electrons.  An atom that loses an electron(s) becomes a positively charged ion since electron are negatively charged.   The reverse is true for an atom that gains an electron(s); it becomes a negatively charged ion.  If you are having trouble following this, it may be helpful to watch the video on ionic and covalent bonds.